Compression screws, such as Herbert screws, are well known in the surgical field. A Herbert screw has a shank that has a smooth section between proximal/trailing and distal/leading threaded sections. The pitch of the distal thread is greater than the pitch of the proximal threads, such that the distal threads advance more rapidly than the proximal threads, resulting in compression. Adjustable compression screws consist of a Herbert-type primary shaft and a separate adjustable head. The adjustable head has an internal thread complementary to the proximal thread of the primary shaft. Rotation of the primary shaft provides primary compression, such as between bone fragments. After primary compression has been achieved, secondary compression can be obtained by rotating the adjustable head separately from the primary shaft, such that the adjustable head threads toward the distal end. U.S. Pat. No. 6,319,254 (Giet), which is incorporated herein by reference, discloses an adjustable compression screw that requires that the adjustable head have an outside thread that has a pitch that is smaller than the pitch of the thread of the screw shank.
Because the adjustable heads of adjustable compression screws have a larger diameter than the primary shaft, it is usually necessary to drill a counterbore for the adjustable head. In the prior art, the counterbore has been formed by drilling a primary bore with a first drill bit, and then forming a counterbore using a second instrument that is configured to drill a counterbore. Alignment of the primary bore and counterbore can be achieved by drilling along a wire. However, the use of separate bits is time consuming and requires multiple instruments. One of the inventions disclosed herein improves on the prior art by combining the primary and counterbore formation into a single adjustable instrument.
One of the other inventions disclosed herein improves on the two part screw driver disclosed in U.S. Pat. No. 6,319,254 (Giet). Giet FIG. 5 shows a set of two screwdrivers 20 and 21 forming respectively a first screwdriver 20 for turning a primary screw shank 1 and a second screwdriver 21 for turning an adjustable head 2. Each screwdriver 20, 21 comprises a respective handle 20A, 21A enabling the screwdriver to be held in the hand for turning purposes. Each handle 20A, 21A is secured to a hollow rod 20B, 21B engaged in the corresponding handle 20A, 21A. The working end of each rod 20B, 21B is provided with two diametrically opposite studs 20C, 21C of the same height and constituting the drive bits of each screwdriver. The diameter of the rod 20B of the first screwdriver is smaller than the diameter of the rod 21B of the second screwdriver 21 so as to enable the first screwdriver 20 to be engaged axially inside the second screwdriver, as shown in particular in Giet FIG. 6. The handles 20A and 21A are likewise shaped so as to be capable of being engaged one relative to the other so as to form a single handle for obtaining a single separable screwdriver instrument, depending on the intended use.
When the screwdrivers are assembled one in the other, the studs 20C and 21C of the rods 20B and 20C are in register with one another (Giet FIG. 6). As shown in FIG. 7, the second screwdriver 21 is provided at its working end portion with an internal setback 22 designed to receive the collar 9 on the screw shank 1 so that it comes into abutment against the end 23 of the setback, which setback is of dimensions that match those of the screw shank 1 The internal setback 22 is of a depth such that when the collar 9 comes into abutment against its end 23 while the screw head 2 is being turned, further turning is automatically prevented before the last turn of the thread 8 is reached so as to ensure that the screw head 2 does not escape from said thread 8. This design feature makes it possible to ensure that the screw does not become separated from its screw head during installation. The inside height of the setback 22 is such that turning of the screw head 2 is interrupted automatically and there is no possibility of subsequent translation movement of the screw head 2 once it is engaged with the thread 8 over the full length of its internal tapping, the respective bottom last turns of the screw head 2 and of the thread 8 preferably then being mutually engaged. This position is shown in Giet FIG. 7, and it serves to retain maximum stability for the screw head 2 since its entire tapping 12 is engaged on the thread 8.
During installation, both screwdrivers 20 and 21 turn together initially (Giet FIG. 6) for the purpose of turning both the screw shank 1 and the screw head 2 until the screw head has been completely buried. Thereafter, the inner screwdriver 20 is withdrawn so that only the outer screwdriver 21 can turn the screw head 2 along the screw shank 1. Under such circumstances, the internal setback 22 prevents the screw head 2 from going beyond the threaded zone, as represented by the thread 8, with the collar 9 coming into abutment against the end 23 of the setback automatically stopping further progress of the screw head 2.
One of the drawbacks of the Giet two-part screwdriver is that the two drivers are separate during use, which makes the screwdriver awkward to use. There is thus a need for a multiuse screwdriver that has the following characteristics and advantages over the prior art.